Expression and regulation of neuropilin-1 in human astrocytomas

The Nervous System Development Regulator Neuropilin-1 as a Potential Prognostic Marker and Therapeutic Target in Brain Cancer

Neuropilins are transmembrane glycoproteins that regulate developmental processes in the nervous system and other tissues. Overexpression of neuropilin-1 (NRP1) occurs in many solid tumor types and, in several instances, may predict patient outcome in terms of overall survival. Experimental inhibition of NRP1 activity can display antitumor effects in different cancer models. Here, we review NRP1 expression and function in adult and pediatric brain cancers, particularly glioblastomas (GBMs) and medulloblastomas, and present analyses of NRP1 transcript levels and their association with patient survival in GBMs. The case of NRP1 highlights the potential of regulators of neurodevelopment as biomarkers and therapeutic targets in brain cancer.

SEMAPHORINS and their receptors: focus on the crosstalk between melanoma and hypoxia

Hypoxia, a condition of oxygen deprivation, is considered a hallmark of tumor microenvironment regulating several pathways and promoting cancer progression and resistance to therapy. Semaphorins, a family of about 20 secreted, transmembrane and GPI-linked glycoproteins, and their cognate receptors (plexins and neuropilins) play a pivotal role in the crosstalk between cancer and stromal cells present in the tumor microenvironment. Many studies reported that some semaphorins are involved in the development of a permissive tumor niche, guiding cell-cell communication and, consequently, the development and progression, as well as the response to therapy, of different cancer histotypes, including melanoma.

In this review we will summarize the state of art of semaphorins regulation by hypoxic condition in cancer with different origin. We will also describe evidence about the ability of semaphorins to affect the expression and activity of transcription factors activated by hypoxia, such as hypoxia-inducible factor-1. Finally, we will focus our attention on findings reporting the role of semaphorins in melanocytes transformation, melanoma progression and response to therapy. Further studies are necessary to understand the mechanisms through which semaphorins induce their effect and to shed light on the possibility to use semaphorins or their cognate receptors as prognostic markers and/or therapeutic targets in melanoma or other malignancies.

Neuropilin: Handyman and Power Broker in the Tumor Microenvironment

Neuropilin-1 and neuropilin-2 form a small family of transmembrane receptors, which, due to the lack of a cytosolic protein kinase domain, act primarily as co-receptors for various ligands. Performing at the molecular level both the executive and organizing functions of a handyman as well as of a power broker, they are instrumental in controlling the signaling of various receptor tyrosine kinases, integrins, and other molecules involved in the regulation of physiological and pathological angiogenic processes. In this setting, the various neuropilin ligands and interaction partners on various cells of the tumor microenvironment, such as cancer cells, endothelial cells, cancer-associated fibroblasts, and immune cells, are surveyed. The suitability of various neuropilin-targeting substances and the intervention in neuropilin-mediated interactions is considered as a possible building block of tumor therapy.

Neuropilin-1 is associated with the prognosis of cervical cancer in Henan Chinese population

Objective: Neuropilin-1 has been reported to be a valuable diagnostic biomarker in patients with cervical intraepithelial neoplasia (CIN) and early cervical cancer. The aim of this study was to investigate the association between Neuropilin-1 and the prognosis of cervical cancer in Henan Chinese population.

Methods: Tissues were collected in The Third Affiliated Hospital of Zhengzhou University between 2010 and 2012, determining the level and expression of Neuropilin-1 in different cervical lesions by immunohistochemistry. The cell proliferation assay, wound-healing assays and Transwell assay were performed to explore the ability of proliferation, migration and invasion for Hela and Caski cells after NRP-1 was knocked down by shRNA transfection. Western blotting was performed to investigate the role of NRP-1 in endothelial-to-mesenchymal transition (EndMT). Tumor xenografts model was used to evaluate the effect of NRP-1 on the tumor growth.

Results: The expression of NRP-1 was upregulated in the tumor tissues compared with the CIN and normal tissues (P<0.0001). The overall survival time of the high NRP-1 expression group was significantly shorter than that of the low NRP-1 expression group (P<0.0001); NRP-1-depleted cells had dramatically lower rate of proliferation, migration and invasion compared to control cells (all P<0.05). Depletion of NRP-1 significantly suppressed the growth of CaSki xenograft tumor in nude mice.

Conclusions: The current study demonstrated that NRP-1 expression is significantly correlated with the progression of CC. Notably, high NRP-1 expression is correlated with a poorer survival in patients with CC, and has been shown to be an independent prognostic factor.

Neuropilins in the Context of Tumor Vasculature

Neuropilin-1 and Neuropilin-2 form a small family of plasma membrane spanning receptors originally identified by the binding of semaphorin and vascular endothelial growth factor. Having no cytosolic protein kinase domain, they function predominantly as co-receptors of other receptors for various ligands. As such, they critically modulate the signaling of various receptor tyrosine kinases, integrins, and other molecules involved in the regulation of physiological and pathological angiogenic processes. This review highlights the diverse neuropilin ligands and interacting partners on endothelial cells, which are relevant in the context of the tumor vasculature and the tumor microenvironment. In addition to tumor cells, the latter contains cancer-associated fibroblasts, immune cells, and endothelial cells. Based on the prevalent neuropilin-mediated interactions, the suitability of various neuropilin-targeted substances for influencing tumor angiogenesis as a possible building block of a tumor therapy is discussed.

Stromal-induced downregulation of miR-1247 promotes prostate cancer malignancy

Cancer progression is strictly dependent on the relationship between tumor cells and the surrounding stroma, which supports cancer malignancy promoting several crucial steps of tumor progression, including the execution of the epithelial to mesenchymal transition (EMT) associated with enhancement in cell invasion, resistance to both anoikis and chemotherapeutic treatments. Recently it has been highlighted the central role of microRNAs (miRNAs) as regulators of tumor progression. Notably, in several tumors a strong deregulation of miRNAs is observed, supporting proliferation, invasion, and metabolic reprogramming of tumor cells. Here we demonstrated that cancer-associated fibroblasts induce a downregulation of miR-1247 in prostate cancer (PCa) cells. We proved that miR-1247 repression is functional for the achievement of EMT and increased cell invasion as well as stemness traits. These phenomena contribute to promote the metastatic potential of PCa cells as demonstrated by increased lung colonization in in vivo experiments. Moreover, as a consequence of miR-1247 downregulation, we observed a correlated increased expression level of neuropilin-1, a miR-1247 target involved as a coreceptor in the epidermal growth factor receptor signaling. Taken together, our data highlight miR-1247 as a potential target for molecular therapies aimed to block the progression and diffusion of PCa.

Neuropilin-1 upregulation elicits adaptive resistance to oncogene-targeted therapies

Cancer cell dependence on activated oncogenes is therapeutically targeted, but acquired resistance is virtually unavoidable. Here we show that the treatment of addicted melanoma cells with BRAF inhibitors, and of breast cancer cells with HER2-targeted drugs, led to an adaptive rise in neuropilin-1 (NRP1) expression, which is crucial for the onset of acquired resistance to therapy. Moreover, NRP1 levels dictated the efficacy of MET oncogene inhibitors in addicted stomach and lung carcinoma cells. Mechanistically, NRP1 induced a JNK-dependent signaling cascade leading to the upregulation of alternative effector kinases EGFR or IGF1R, which in turn sustained cancer cell growth and mediated acquired resistance to BRAF, HER2, or MET inhibitors. Notably, the combination with NRP1-interfering molecules improved the efficacy of oncogene-targeted drugs and prevented or even reversed the onset of resistance in cancer cells and tumor models. Our study provides the rationale for targeting the NRP1-dependent upregulation of tyrosine kinases, which are responsible for loss of responsiveness to oncogene-targeted therapies.

Effects of hypoxia and hyperoxia on the differential expression of VEGF-A isoforms and receptors in Idiopathic Pulmonary Fibrosis (IPF)

Dysregulation of VEGF-A bioavailability has been implicated in the development of lung injury/fibrosis, exemplified by Idiopathic Pulmonary Fibrosis (IPF). VEGF-A is a target of the hypoxic response via its translational regulation by HIF-1α. The role of hypoxia and hyperoxia in the development and progression of IPF has not been explored. In normal lung (NF) and IPF-derived fibroblasts (FF) VEGF-A_xxxa protein expression was upregulated by hypoxia, mediated through activation of VEGF-A_xxxa gene transcription. VEGF-A receptors and co-receptors were differentially expressed by hypoxia and hyperoxia. Our data supports a potential role for hypoxia, hyperoxia and VEGF-A_xxxa isoforms as drivers of fibrogenesis.

The Neuropilins and Their Ligands in Hematogenous Metastasis of Salivary Adenoid Cystic Carcinoma-An Immunohistochemical Study

PURPOSE

We investigated the expression of neuropilin-1 (NRP1), neuropilin-2 (NRP2), vascular endothelial growth factor-A (VEGF-A), semaphorin-3A (Sema-3A), and semaphorin-3F (Sema-3F) in normal salivary gland (NSG) tissue, nonmetastatic salivary adenoid cystic carcinoma (SACC), and metastatic SACC to better understand their role in intratumoral angiogenesis and hematogenous metastasis of SACC.

PATIENTS AND METHODS

The study included 60 SACC patients, equally divided between nonmetastatic SACC and metastatic SACC. We used 30 NSG samples as the control. The expression of cytokines was studied by immunohistochemistry and compared using the integrated optical density. The relationship between NRP1, NRP2, VEGF-A, and Sema-3A expression and microvessel density (MVD) was analyzed in the 3 groups.

RESULTS

In metastatic SACC, the expression levels of NRP1 and VEGF-A were significantly greater than those in nonmetastatic SACC and NSG. The expression of Sema-3A and Sema-3F was significantly lower in metastatic SACC than that in nonmetastatic SACC and NSG (P < .0001). No significant differences were found in NRP2 expression among the 3 groups (P = .43). The MVD of metastatic SACC was significantly greater than that of nonmetastatic SACC and NSG (P < .0001). However, the lymphatic vessel density of the 3 groups was not significantly different statistically. The relationship between MVD and NRP1 or VEGF-A showed a significant positive correlation (P < .0001, for both). However, a significant negative correlation was found between the MVD and Sema-3A or Sema-3F expression (P < .0001, for both).

CONCLUSIONS

Hematogenous metastasis of SACC is correlated with high expression of NRP1 and VEGF-A and low expression of Sema-3A and Sema-3F. The increased numbers of microvessels induced by VEGF-A signaling, combined with NRP1, could be one of the key reasons leading to the enhanced hematogenous metastasis in SACC.

Increased ratio of vascular endothelial growth factor to semaphorin3A is a negative prognostic factor in human meningiomas

Semaphorin3A (SEMA3A) is an anti-angiogenic factor which is expressed in human meningiomas in association with low microvessel density (MVD). It competes with vascular endothelial growth factor (VEGF) for receptor neuropilin-1 (NRP-1). The ratio between VEGF and SEMA3A has been recently demonstrated to regulate neo-angiogenesis, proliferation and progression of tumors. To clarify the involvement of these proteins in the above-mentioned phenomena, we analyzed the immunohistochemical expression of SEMA3A, VEGF and NRP-1 and their correlation with MVD in a series of 48 cases of meningioma with different histotype and histological grade. SEMA3A and VEGF expression was encountered in about half the cases, although at different levels. NRP-1 staining was evidenced in the vessels within all but two tumors and in the neoplastic cells of 18/48 meningiomas. A negative significant correlation emerged between SEMA3A amount and MVD; on the other hand, high VEGF levels appeared to be significantly associated with high MVD. A high VEGF/SEMA3A was significantly associated with high histological grade, proliferation index and MVD as well as with a higher recurrence rate of the meningiomas. Present data suggest that the balance between the expression of the pro-angiogenic factor VEGF and the anti-angiogenic SEMA3A may be involved in the regulation of neo-angiogenesis and proliferation in meningiomas, representing also a predictor of recurrences in these tumors. Further validation of our results may open the way for the use of drugs targeting not only VEGF, but also NRP-1 and SEMA3A to prevent recurrences of meningiomas.

Genome-wide analysis reveals NRP1 as a direct HIF1α-E2F7 target in the regulation of motorneuron guidance in vivo

In this study, we explored the existence of a transcriptional network co-regulated by E2F7 and HIF1α, as we show that expression of E2F7, like HIF1α, is induced in hypoxia, and because of the previously reported ability of E2F7 to interact with HIF1α. Our genome-wide analysis uncovers a transcriptional network that is directly controlled by HIF1α and E2F7, and demonstrates both stimulatory and repressive functions of the HIF1α -E2F7 complex. Among this network we reveal Neuropilin 1 (NRP1) as a HIF1α-E2F7 repressed gene. By performing in vitro and in vivo reporter assays we demonstrate that the HIF1α-E2F7 mediated NRP1 repression depends on a 41 base pairs ‘E2F-binding site hub’, providing a molecular mechanism for a previously unanticipated role for HIF1α in transcriptional repression. To explore the biological significance of this regulation we performed in situ hybridizations and observed enhanced nrp1a expression in spinal motorneurons (MN) of zebrafish embryos, upon morpholino-inhibition of e2f7/8 or hif1α. Consistent with the chemo-repellent role of nrp1a, morpholino-inhibition of e2f7/8 or hif1α caused MN truncations, which was rescued in TALEN-induced nrp1a^hu10012 mutants, and phenocopied in e2f7/8 mutant zebrafish. Therefore, we conclude that repression of NRP1 by the HIF1α-E2F7 complex regulates MN axon guidance in vivo.

Circulating soluble neuropilin-1 in patients with early cervical cancer and cervical intraepithelial neoplasia can be used as a valuable diagnostic biomarker

Objective. To investigate soluble neuropilin-1 (sNRP-1) in circulating and NRP-1 protein in cervical tissues from patients with cervical cancer or cervical intraepithelial neoplasia (CIN). Methods. sNRP-1 was measured in 64 preoperative patients and 20 controls. NRP-1 protein in cervical tissue was detected in 56 patients and 20 controls. Results. Both sNRP-1 and NRP-1 proteins were correlated with stage. sNRP-1 presented a high diagnostic ability of cervical cancer and CIN, with a sensitivity of 70.97% and a specificity of 73.68%. Conclusions. sNRP-1 in circulating can serve as a possible valuable diagnostic biomarker for cervical cancer and CIN.

NRP-1 expression in bladder cancer and its implications for tumor progression

Neuropilin-1 (NRP-1) overexpression has been reported in a variety of human cancers. However, the role of NRP-1 in bladder cancer (BC) remains unclear. The aim of present study was to analyze NRP-1 protein expression in BC tissues and to assess its prognostic significance for BC. NRP-1 messenger ribonucleic acid (mRNA) and protein expression were determined by real-time quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) and immunohistochemistry in specimens of primary cancer and their adjacent noncancerous tissues in BC patients. Additionally, NRP-1 protein expression in 139 archived paraffin-embedded BC samples was analyzed by immunohistochemistry and correlated with clinicopathological characteristics and survival. Student's t test, Spearman's rank correlation, Kaplan-Meier plots, and Cox's proportional hazards regression model were used to analyze the data. By qRT-PCR and immunohistochemistry, the levels of NRP-1 mRNA and protein were significantly higher in BC, compared to that in adjacent noncancerous tissues (P<0.001). High expression of NRP-1 was significantly associated with histologic grade (P=0.016) and tumor stage (P=0.001). Multivariate analysis showed that high expression of NRP-1 was an independent prognostic factor for overall survival. Our study suggests that overexpression of NRP-1 may play an important role in the progression of BC, and NRP-1 expression may serve as a biomarker for poor prognosis for BC.

Co-administration of dual-targeting nanoparticles with penetration enhancement peptide for antiglioblastoma therapy

Chemotherapy is an indispensable auxiliary treatment for glioma but highly limited by the existence of both blood-brain barrier (BBB) and blood-brain tumor barrier (BBTB). The dysfunctional brain tumor blood vessels and high interstitial pressure in glioma also greatly hindered the accumulation and deep penetration of chemotherapeutics into the glioma. Lactoferrin (Lf), with its receptor overexpressed on both the brain endothelial cells and glioma cells, was here functionalized to the surface of poly(ethylene glycol)-poly(lactic acid) nanoparticles to mediate BBB/BBTB and glioma cell dual targeting. tLyP-1, a tumor-homing peptide, which contains a C-end Rule sequence that can mediate tissue penetration through the neuropilin-1-dependent internalization pathway, was coadministrated with Lf-functionalized nanoparticles (Lf-NP) to enhance its accumulation and deep penetration into the glioma parenchyma. Enhanced cellular association in both BCEC and C6 cells, increased cytotoxicity of the loaded paclitaxel, and deep penetration in the 3D glioma spheroids was achieved by Lf-NP. Following coadministration with tLyP-1, the functionalized nanoparticles obtained improved tumor targeting, glioma vascular extravasation, and antiglioma efficacy. The findings here suggested that the strategy by coadministrating BBB/BBTB and glioma cells dual-targeting nanocarriers with a tumor penetration enhancement peptide represent a promising platform for antiglioma drug delivery.

VEGF targets the tumour cell

The function of vascular endothelial growth factor (VEGF) in cancer is not limited to angiogenesis and vascular permeability. VEGF-mediated signalling occurs in tumour cells, and this signalling contributes to key aspects of tumorigenesis, including the function of cancer stem cells and tumour initiation. In addition to VEGF receptor tyrosine kinases, the neuropilins are crucial for mediating the effects of VEGF on tumour cells, primarily because of their ability to regulate the function and the trafficking of growth factor receptors and integrins. This has important implications for our understanding of tumour biology and for the development of more effective therapeutic approaches.

Neuropilin-1 in transplantation tolerance

In the immune system, Neuropilin-1 (Nrp1) is a molecule that plays an important role in establishing the immunological synapse between dendritic cells (DCs) and T cells. Recently, Nrp1 has been identified as a marker that seems to distinguish natural T regulatory (nTreg) cells, generated in the thymus, from inducible T regulatory (iTreg) cells raised in the periphery. Given the crucial role of both nTreg and iTreg cells in the generation and maintenance of immune tolerance, the ability to phenotypically identify each of these cell populations in vivo is needed to elucidate their biological properties. In turn, these properties have the potential to be developed for therapeutic use to promote immune tolerance. Here we describe the nature and functions of Nrp1, including its potential use as a therapeutic target in transplantation tolerance.

Neuropilin-1-dependent regulation of EGF-receptor signaling

Neuropilin-1 (NRP1) is a coreceptor for multiple extracellular ligands. NRP1 is widely expressed in cancer cells and in advanced human tumors; however, its functional relevance and signaling mechanisms are unclear. Here, we show that NRP1 expression controls viability and proliferation of different cancer cells, independent of its short intracellular tail. We found that the extracellular domain of NRP1 interacts with the EGF receptor (EGFR) and promotes its signaling cascade elicited upon EGF or TGF-α stimulation. Upon NRP1 silencing, the ability of ligand-bound EGFR to cluster on the cell surface, internalize, and activate the downstream AKT pathway is severely impaired. EGFR is frequently activated in human tumors due to overexpression, mutation, or sustained autocrine/paracrine stimulation. Here we show that NRP1-blocking antibodies and NRP1 silencing can counteract ligand-induced EGFR activation in cancer cells. Thus our findings unveil a novel molecular mechanism by which NRP1 can control EGFR signaling and tumor growth.

Transcriptional profiling of human glioblastoma vessels indicates a key role of VEGF-A and TGFβ2 in vascular abnormalization

Glioblastoma are aggressive astrocytic brain tumours characterized by microvascular proliferation and an abnormal vasculature, giving rise to brain oedema and increased patient morbidity. Here, we have characterized the transcriptome of tumour-associated blood vessels and describe a gene signature clearly associated with pleomorphic, pathologically altered vessels in human glioblastoma (grade IV glioma). We identified 95 genes differentially expressed in glioblastoma vessels, while no significant differences in gene expression were detected between vessels in non-malignant brain and grade II glioma. Differential vascular expression of ANGPT2, CD93, ESM1, ELTD1, FILIP1L and TENC1 in human glioblastoma was validated by immunohistochemistry, using a tissue microarray. Through qPCR analysis of gene induction in primary endothelial cells, we provide evidence that increased VEGF-A and TGFβ2 signalling in the tumour microenvironment is sufficient to invoke many of the changes in gene expression noted in glioblastoma vessels. Notably, we found an enrichment of Smad target genes within the distinct gene signature of glioblastoma vessels and a significant increase of Smad signalling complexes in the vasculature of human glioblastoma in situ. This indicates a key role of TGFβ signalling in regulating vascular phenotype and suggests that, in addition to VEGF-A, TGFβ2 may represent a new target for vascular normalization therapy.

Neuropilin-1 is upregulated in hepatocellular carcinoma and contributes to tumour growth and vascular remodelling

BACKGROUND & AIMS

Neuropilin-1 (NRP1) is a transmembrane co-receptor for semaphorins and heparin-binding pro-angiogenic cytokines, principally members of the vascular endothelial growth factor family. Recent studies revealed an important role of NRP1 in angiogenesis and malignant progression of many cancers. The role of NRP1 in the development of hepatocellular carcinoma (HCC) is not completely understood.

METHODS

We used human tissue microarrays and a mouse transgenic model of HCC to establish the spatio-temporal patterns of NRP1 expression in HCC. To evaluate the therapeutic potential of targeting NRP1 in HCC, we treated HCC mice with peptide N, an NRP1 binding recombinant protein and competitive inhibitor of the VEGF-A(165)/NRP1 interaction.

RESULTS

We demonstrate that NRP1 is expressed in hepatic endothelial cells of both human healthy biopsies and in HCC samples, but not in normal hepatocytes. We found that increased NRP1 expression in human tumour hepatocytes is significantly associated with primary HCC. Using RT-PCR, Western blot and immunofluorescence analysis we show that NRP1 expression in the liver of transgenic HCC mice is increased with disease progression, in both vascular and tumour compartments. Blocking NRP1 function with peptide N leads to the inhibition of vascular remodelling and tumour liver growth in HCC mice.

CONCLUSIONS

Our results indicate a specific role of NRP1 in HCC growth and vascular remodelling and highlight the possibility of therapeutically targeting NRP1 for the treatment of HCC.

Semaphorin 3A lytic hybrid peptide binding to neuropilin-1 as a novel anti-cancer agent in pancreatic cancer

We previously reported that novel targeted "hybrid peptide" in which epidermal growth factor receptor (EGFR) binding peptide was conjugated with lytic-type peptide had selective cytotoxic activity to EGFR expressing cancer cells. In this study, we have generated a novel type hybrid peptide, semaphorin 3A lytic (Sema3A-lytic), which is composed of two functional amino acid domains: a sequence derived from Sema3A that binds to neuropilin-1 (NRP1) and a cytotoxic lytic peptide. We found that this hybrid peptide had cytotoxic activity against NRP1-positive pancreatic cancer cell lines such as BxPC-3 and Panc-1, whereas the peptide did not affect the viability of normal cells in vitro. It was also found by affinity analysis that Sema3A peptide binds to NRP1, and two arginines (372R and 377R) in Sema3A peptide are involved in the interaction with NRP1 protein. In addition, confocal microscopy analysis revealed that Sema3A-lytic peptide could not penetrate normal cells regardless of the presence of NRP1 mRNA, suggesting that the ability of Sema3A-lytic peptide to concentrate adjacent to the cell membrane by binding to NRP1 with the target-binding moiety contributes to its selective cytotoxic activity. These results indicate that Sema3A-lytic hybrid peptide would be a possible anti-cancer agent for treatment of human pancreatic cancer.

Hypoxia induces tumor and endothelial cell migration in a semaphorin 3F- and VEGF-dependent manner via transcriptional repression of their common receptor neuropilin 2

Neuropilin-2 (NRP2) is a receptor expressed by tumor cells and endothelial cells (EC) that binds both semaphorin 3F (SEMA3F), a potent inhibitor of tumor angiogenesis and metastasis, and vascular endothelial growth factor (VEGF), a potent stimulator of tumor angiogenesis. It was found that glioblastoma and melanoma cells repressed NRP2 expression when maintained under hypoxic conditions and after treatment with the hypoxia-mimetic agent desferrioxamine (DFO), at both the mRNA and protein levels. Silencing of HIF1-α, the hypoxia-induced subunit of the hypoxia inducible factor (HIF), abrogated DFO-induced NRP2 repression. Conversely, ectopic expression of HIF1-α directly repressed NRP2 promoter activity and expression. NRP2 is the sole receptor for SEMA3F. Loss of NRP2 expression in tumor cells inhibited SEMA3F-dependent activities, such as inactivation of RhoA, depolymerization of F-actin, and inhibition of tumor cell migration. On the other hand, loss of NRP2 expression in tumor cells increased VEGF protein levels in conditioned media, with no effects on VEGF mRNA levels. This increase in VEGF protein levels promoted paracrine activation of EC, including VEGF receptor-2 phosphorylation, and activation of downstream signaling proteins such as p44/42 MAPK and p38 MAPK. In addition, the elevated VEGF levels induced EC migration and sprouting, two key steps of tumor angiogenesis in vivo. It was concluded that hypoxia regulates VEGF and SEMA3F activities through transcriptional repression of their common receptor NRP2, providing a novel mechanism by which hypoxia induces tumor angiogenesis, growth and metastasis.

Neuropilins: a new target for cancer therapy

Recent investigations highlighted strong similarities between neural crest migration during embryogenesis and metastatic processes. Indeed, some families of axon guidance molecules were also reported to participate in cancer invasion: plexins/semaphorins/neuropilins, ephrins/Eph receptors, netrin/DCC/UNC5. Neuropilins (NRPs) are transmembrane non tyrosine-kinase glycoproteins first identified as receptors for class-3 semaphorins. They are particularly involved in neural crest migration and axonal growth during development of the nervous system. Since many types of tumor and endothelial cells express NRP receptors, various soluble molecules were also found to interact with these receptors to modulate cancer progression. Among them, angiogenic factors belonging to the Vascular Endothelial Growth Factor (VEGF) family seem to be responsible for NRP-related angiogenesis. Because NRPs expression is often upregulated in cancer tissues and correlated with poor prognosis, NRPs expression might be considered as a prognostic factor. While NRP1 was intensively studied for many years and identified as an attractive angiogenesis target for cancer therapy, the NRP2 signaling pathway has just recently been studied. Although NRP genes share 44% homology, differences in their expression patterns, ligands specificities and signaling pathways were observed. Indeed, NRP2 may regulate tumor progression by several concurrent mechanisms, not only angiogenesis but lymphangiogenesis, epithelial-mesenchymal transition and metastasis. In view of their multiples functions in cancer promotion, NRPs fulfill all the criteria of a therapeutic target for innovative anti-tumor therapies. This review focuses on NRP-specific roles in tumor progression.

Semaphorin, neuropilin and VEGF expression in glial tumours: SEMA3G, a prognostic marker?

Gliomas are characterised by local infiltration, migration of tumour cells across long distances and sustained angiogenesis; therefore, proteins involved in these processes are most likely important. Such candidates are semaphorins involved in axon guidance and cell migration. In addition, semaphorins regulate tumour progression and angiogenesis. For cell signalling, class-4 semaphorins bind directly to plexins, whereas class-3 semaphorins require additional neuropilin (NRP) receptors that also bind VEGF₁₆₅. The anti-angiogenic activity of class-3 semaphorins can be explained by competition with VEGF₁₆₅ for NRP binding. In this study, we analysed the expressions of seven semaphorins of class-3, SEMA4D, VEGF and the NRP1 and NRP2 receptors in 38 adult glial tumours. In these tumours, SEMA3B, SEMA3G and NRP2 expressions were related to prolonged survival. In addition, SEMA3D expression was reduced in high-grade as compared with low-grade gliomas. In contrast, VEGF correlated with higher grade and poor survival. Thus, our data suggest a function for a subset of class-3 semaphorins as inhibitors of tumour progression, and the prognostic value of the VEGF/SEMA3 balance in adult gliomas. Moreover, in multivariate analysis, SEMA3G was found to be the only significant prognostic marker.

The direct effects of anti-vascular endothelial growth factor therapy on tumor cells

The vascular endothelial growth factor (VEGF) family members are essential mediators of tumor angiogenesis. The multiple functions of the VEGFs are mediated through complex interactions between their ligands, the high-affinity tyrosine kinase receptors, and co-receptors (neuropilins). Emerging evidence has shown that these receptors, formerly described as being exclusively expressed on endothelial cells, are also expressed on a number of nonendothelial cells, including tumor cells. Moreover, it has been shown that their receptors (VEGFRs) are functional in a number of nonendothelial systems, where they can serve as targets for anti-VEGF therapy. As the expression of VEGFRs on tumor cells contributes to the understanding of the complex roles of VEGF within the tumor microenvironment and elucidation of VEGF activity might further refine antineoplastic regimens, this article will review the main effects and selective interactions of the VEGFRs, the evidence for their expression and function on tumor cells, and the direct efforts of anti-VEGF therapy on tumor cells.

Neuropilin-1 promotes unlimited growth of ovarian cancer by evading contact inhibition

OBJECTIVE

Neuropilin-1 (NRP-1) is a receptor for both semaphorin and vascular endothelial growth factor and is up-regulated in a variety of human cancers. While there are some reports of NRP-1 expression in ovarian neoplasm, those results differ in pattern of its expression and its role in ovarian cancer is still unclear. We sought to investigate the expression pattern and role of NRP-1 in ovarian cancer.

METHODS

NRP-1 expression was analyzed with eighty-seven ovarian tissue samples by immunohistochemistry and four ovarian cell lines by quantitative RT-PCR and Western blotting. To detect its molecular role in ovarian cancer, WST-1 assay, invasion assay and soft agar assay were performed with or without NRP-1 suppression by the introduction of short hairpin RNAs.

RESULTS

NRP-1 expression was found to be enhanced in ovarian cancer compared with ovarian surface epithelium (OSE), benign adenoma and tumors of low malignant potential. In vitro, NRP-1 expression was augmented threefold during malignant transformation of OSE cells with oncogene ras, suggesting an association between NRP-1 and oncogenesis. Suppression of NRP-1 reduced cell proliferation in a dense state, indicating that persistently high expression of NRP-1 in ovarian cancer enhances proliferation through evasion of contact inhibition. Suppression of NRP-1 also decreased cell growth in soft agar and invasion to the extracellular matrix in vitro.

CONCLUSIONS

These results suggest that NRP-1 is not only associated with oncogenesis, but also with ovarian cancer malignancy, and this molecule is a targeting candidate for the treatment of ovarian malignancies.

Neuropilin-1 promotes human glioma progression through potentiating the activity of the HGF/SF autocrine pathway

Neuropilin-1 (NRP1) functions as a coreceptor through interaction with plexin A1 or vascular endothelial growth factor (VEGF) receptor during neuronal development and angiogenesis. NRP1 potentiates the signaling pathways stimulated by semaphorin 3A and VEGF-A in neuronal and endothelial cells, respectively. In this study, we investigate the role of tumor cell-expressed NRP1 in glioma progression. Analyses of human glioma specimens (WHO grade I-IV tumors) revealed a significant correlation of NRP1 expression with glioma progression. In tumor xenografts, overexpression of NRP1 by U87MG gliomas strongly promoted tumor growth and angiogenesis. Overexpression of NRP1 by U87MG cells stimulated cell survival through the enhancement of autocrine hepatocyte growth factor/scatter factor (HGF/SF)/c-Met signaling. NRP1 not only potentiated the activity of endogenous HGF/SF on glioma cell survival but also enhanced HGF/SF-promoted cell proliferation. Inhibition of HGF/SF, c-Met and NRP1 abrogated NRP1-potentiated autocrine HGF/SF stimulation. Furthermore, increased phosphorylation of c-Met correlated with glioma progression in human glioma biopsies in which NRP1 is upregulated and in U87MG NRP1-overexpressing tumors. Together, these data suggest that tumor cell-expressed NRP1 promotes glioma progression through potentiating the activity of the HGF/SF autocrine c-Met signaling pathway, in addition to enhancing angiogenesis, suggesting a novel mechanism of NRP1 in promoting human glioma progression.

Vascular endothelial growth factor (VEGF) signaling in tumor progression

Vascular endothelial cells are ordinarily quiescent in adult humans and divide less than once per decade. When tumors reach a size of about 0.2-2.0mm in diameter, they become hypoxic and limited in size in the absence of angiogenesis. There are about 30 endogenous pro-angiogenic factors and about 30 endogenous anti-angiogenic factors. In order to increase in size, tumors undergo an angiogenic switch where the action of pro-angiogenic factors predominates, resulting in angiogenesis and tumor progression. One mechanism for driving angiogenesis results from the increased production of vascular endothelial growth factor (VEGF) following up-regulation of the hypoxia-inducible transcription factor. The human VEGF family consists of VEGF (VEGF-A), VEGF-B, VEGF-C, VEGF-D, and placental growth factor (PlGF). The VEGF family of receptors consists of three protein-tyrosine kinases and two non-protein kinase receptors (neuropilin-1 and -2). Owing to the importance of angiogenesis in tumor progression, inhibition of VEGF signaling represents an attractive cancer treatment.

Neuropilins in physiological and pathological angiogenesis

Neuropilin-1 (Np1) and neuropilin-2 (Np2) are transmembrane glycoproteins with large extracellular domains that interact with both class 3 semaphorins and vascular endothelial growth factor (VEGF), and are involved in the regulation of many physiological pathways, including angiogenesis. The neuropilins also interact directly with the classical receptors for VEGF, VEGF-R1 and -R2, mediating signal transduction. The heart, glomeruli and osteoblasts express both Np1 and Np2, but there is differential expression in the adult vasculature, with Np1 expressed mainly by arterial endothelium, whereas Np2 is only expressed by venous and lymphatic endothelium. Both neuropilins are commonly over-expressed in regions of physiological (wound-healing) and pathological (tumour) angiogenesis, but the signal transduction pathways, neuropilin-mediated gene expression and the definitive role of neuropilins in angiogenic processes are not fully characterized. This review details the current evidence for the role of neuropilins in angiogenesis, and suggests future research directions that may enhance our understanding of the mechanisms of action of this unique family of proteins.

Gene-linked shift in ganglioside distribution influences growth and vascularity in a mouse astrocytoma

Brain tumor growth and progression is dependent upon vascularity, and is associated with altered ganglioside composition and distribution. In this study, we examined the influence of gangliosides on growth and vascularity in a malignant mouse astrocytoma, CT-2A. Ganglioside distribution was altered in CT-2A tumor cells using an antisense construct to beta-1,4-N-acetylgalactosaminyltransferase (GalNAc-T), a key enzyme that uses the simple ganglioside GM3 as a substrate for the synthesis of the more complex gangliosides, GM2, GM1 and GD1a. GalNAc-T gene expression was significantly lower in CT-2A cells stably transfected with the antisense GalNAc-T plasmid, pcDNA3.1/TNG (CT-2A/TNG) than in either non-transfected CT-2A or mock-transfected (CT-2A/V) control tumor cells. GM3 was elevated from 16% to 58% of the total ganglioside distribution, whereas GM1 and GD1a were reduced from 17% and 49% to 10% and 17%, respectively, in CT-2A/TNG tumor cells. Growth, vascularity (blood vessel density and Matrigel assay) and vascular endothelial growth factor (VEGF) expression was significantly less in CT-2A/TNG tumors than in control CT-2A brain tumors. In addition, the expression of VEGF, hypoxia-inducible factor 1alpha (HIF-1alpha) and neuropilin-1 (NP-1) was significantly lower in CT-2A/TNG tumor cells than in control CT-2A tumor cells. These data suggest that gene-linked changes in ganglioside composition influence the growth and angiogenic properties of the CT-2A astrocytoma.

The role of neuropilins in cancer

Neuropilins are multifunctional non-tyrosine kinase receptors that bind to class 3 semaphorins and vascular endothelial growth factor. NRP-1 and NRP-2 were first identified for their key role in mediating axonal guidance in the developing nervous system through their interactions with class 3 semaphorins. Growing evidence supports a critical role for these receptors in tumor progression. Neuropilin expression is up-regulated in multiple tumor types, and correlates with tumor progression and prognosis in specific tumors. Neuropilins may indirectly mediate effects on tumor progression by affecting angiogenesis or directly through effects on tumor cells. This article reviews emerging evidence for the role of neuropilins in tumor biology. The therapeutic implications of these data are far-reaching and suggest that neuropilin-targeted interventions may be useful as a component of antineoplastic therapy.

Angiogenic and cell survival functions of vascular endothelial growth factor (VEGF)

Vascular endothelial growth factor (VEGF) was originally identified as an endothelial cell specific growth factor stimulating angiogenesis and vascular permeability. Some family members, VEGF C and D, are specifically involved in lymphangiogenesis. It now appears that VEGF also has autocrine functions acting as a survival factor for tumour cells protecting them from stresses such as hypoxia, chemotherapy and radiotherapy. The mechanisms of action of VEGF are still being investigated with emerging insights into overlapping pathways and cross-talk between other receptors such as the neuropilins which were not previously associated with angiogenesis. VEGF plays an important role in embryonic development and angiogenesis during wound healing and menstrual cycle in the healthy adult. VEGF is also important in a number of both malignant and non-malignant pathologies. As it plays a limited role in normal human physiology, VEGF is an attractive therapeutic target in diseases where VEGF plays a key role. It was originally thought that in pathological conditions such as cancer, VEGF functioned solely as an angiogenic factor, stimulating new vessel formation and increasing vascular permeability. It has since emerged it plays a multifunctional role where it can also have autocrine pro-survival effects and contribute to tumour cell chemoresistance. In this review we discuss the established role of VEGF in angiogenesis and the underlying mechanisms. We discuss its role as a survival factor and mechanisms whereby angiogenesis inhibition improves efficacy of chemotherapy regimes. Finally, we discuss the therapeutic implications of targeting angiogenesis and VEGF receptors, particularly in cancer therapy.

A peptide competing with VEGF165 binding on neuropilin-1 mediates targeting of a chlorin-type photosensitizer and potentiates its photodynamic activity in human endothelial cells

Destruction of the neovasculature is essential for efficient tumor eradication by photodynamic therapy (PDT). Since the over-expression of receptors for vascular endothelial growth factor (VEGF) is correlated with tumor angiogenesis and subsequent growth, we conjugated a photosensitizer (5-(4-carboxyphenyl)-10,15,20-triphenyl-chlorin, TPC), via a spacer (6-aminohexanoic acid, Ahx), to a VEGF receptor-specific heptapeptide (ATWLPPR). ATWLPPR and TPC-Ahx-ATWLPPR bound exclusively to neuropilin-1 (NRP-1) recombinant chimeric protein (IC50=19 and 171 microM, respectively) but were devoid of affinity for VEGF receptor type 2 (VEGFR-2, KDR), to which ATWLPPR was initially thought to bind. TPC-Ahx-ATWLPPR was incorporated up to 25-fold more in human umbilical vein endothelial cells (HUVEC) than TPC over a 24-h period, and the addition of 8 mM ATWLPPR induced a significant decrease of this uptake (P<0.05), corroborating a receptor-mediated incorporation. Slightly less cytotoxic in the dark, TPC-Ahx-ATWLPPR exhibited enhanced in vitro photodynamic activity (10.4-fold), compared to TPC. Pharmacokinetic analysis in nude mice xenografted with U87 human malignant glioma cells revealed relevant tumor levels as soon as 1 h after intravenous injection of TPC-Ahx-ATWLPPR, and a rapid elimination from the blood compartment. Moreover, TPC-Ahx-ATWLPPR was not degraded in vivo up to 2 h after intravenous injection. Taken together, our results demonstrate that TPC-Ahx-ATWLPPR is a much more potent photosensitizer in vitro than TPC, in NRP-1-expressing cells. Thus, it may efficiently potentiate the vascular effect of PDT in vivo.

Angiogenesis in gliomas: biology and molecular pathophysiology

Glioblastoma multiforme (GBM) is characterized by exuberant angiogenesis, a key event in tumor growth and progression. The pathologic mechanisms driving this change and the biological behavior of gliomas remain unclear. One mechanism may involve cooption of native blood vessels by glioma cells inducing expression of angiopoietin-2 by endothelial cells. Subsequently, vascular apoptosis and involution leads to necrosis and hypoxia. This in turn induces angiogenesis that is associated with expression of hypoxia-inducible factor (HIF)-1alpha and vascular endothelial growth factor (VEGF) in perinecrotic pseudopalisading glioma cells. Here we review the molecular and cellular mechanisms implicated in HIF-1-dependent and HIF-1-independent glioma-associated angiogenesis. In GBMs, both tumor hypoxia and genetic alterations commonly occur and act together to induce the expression of HIF-1. The angiogenic response of the tumor to HIF-1 is mediated by HIF-1-regulated target genes leading to the upregulation of several proangiogenic factors such as VEGF and other adaptive response molecules. Understanding the roles of these regulatory processes in tumor neovascularization, tumor growth and progression, and resistance to therapy will ultimately lead to the development of improved antiangiogenic therapies for GBMs.

The molecular orchestra of the migration of oligodendrocyte precursors during development

During development of the central nervous system (CNS), postmitotic cells (including neurons and myelin-generating cells, the oligodendrocytes) migrate from the germinal areas of the neural tube where they originate to their final destination sites. The migration of neurons during development has been extensively studied and has been the topic of detailed reviews. The migration of oligodendrocyte precursor cells (OPCs) is also an extremely complex and precise event, with a widespread migration of OPCs across many regions to colonize the entire CNS. Different mechanisms have been shown to direct the migration of OPCs, among them contact-mediated mechanisms (adhesion molecules) and long-range cues (chemotropic molecules). This review provides a detailed overview and discussion of the cellular and molecular basis of OPCs migration during development. Because it has been shown that neuronal and oligodendroglial lineages share some of these mechanisms, we briefly summarize similarities and differences between these two types of neural cells. We also summarize the changes in the normal migration of OPCs during development that would be relevant for different neurological diseases (including demyelinating diseases, such as multiple sclerosis, and glial cancers). We also examine the relevance of these migratory properties of the oligondendrocytic cell lineage for the repair of neural damage.

Upregulation of neuropilin-1 by basic fibroblast growth factor enhances vascular smooth muscle cell migration in response to VEGF

Neuropilin-1 (NRP-1) is a co-receptor for vascular endothelial growth factor (VEGF). During neovascularization, vascular smooth muscle cells (VSMCs) and pericytes modulate the function of endothelial cells. Factors that mediate NRP-1 in human VSMCs (hVSMCs) remain to be elucidated. We studied various angiogenic cytokines to identify factors that increase NRP-1 expression in hVSMCs. Treatment of hVSMCs with basic fibroblast growth factor (b-FGF) induced expressions of NRP-1 mRNA and protein whereas epidermal growth factor, insulin-like growth factor-1, and interleukin-1beta did not. b-FGF induced phosphorylation of Erk-1/2 and JNK. MEK1/2 and nuclear factor kappa B (NF-kappaB) inhibitors (U0126 and TLCK, respectively) blocked the ability of b-FGF to induce NRP-1 mRNA expression, but inhibition of JNK (SP600125) or PI3-kinase activity (wortmannin) did not. Further, the increase in NRP-1 expression by b-FGF enhanced hVSMCs migration in response to VEGF(165). This effect was dependent on the binding of VEGF(165) to VEGFR-2, as blocking antibodies to VEGFR-2, but not VEGFR-1, inhibited VEGF(165)-induced migration. In conclusion, b-FGF increased NRP-1 expression in hVSMCs that in turn enhance the effect of VEGF(165) on cell migration. The enhanced migration of hVSMCs was mediated through binding of VEGF(165) to both NRP-1 and VEGFR-2, as inhibition of VEGFR-2 on these cells blocked the effect of VEGF-mediated cell migration.

Roles of neuropilins in neuronal development, angiogenesis, and cancers

Neuropilin-1 (NRP1) and neuropilin-2 (NRP2) are transmembrane glycoproteins that have been characterized as receptors for both semaphorins for neuronal guidance and vascular endothelial growth factor (VEGF) for angiogenesis. Biologic properties of NRPs have been linked to their unique domain structures. However, molecular interaction among NRPs, VEGF, and VEGF receptors is still not clear. Although several types of cancer cells can express NRPs, the role of NRPs in tumor pathogenesis is largely unknown. Thus, future investigations should include determining the effects and mechanisms of NRPs on proliferation, apoptosis, and migration of neuronal , endothelial, and cancer cells. Study of protein-protein interaction, signal transduction pathways, and NRP-mediated gene expression is particularly important to understand NRPs functions, which may have significant clinical applications in the treatment of neurological disorders, cardiovascular diseases, and certain cancers.

Role of Ang1 and its interaction with VEGF-A in astrocytomas

Angiopoietins (Ang1 and Ang2) modulate the activity of the endothelial cell (EC)-specific receptor tyrosine kinase Tie2, which together with vascular endothelial growth factor (VEGF-A) and its EC-specific receptors, VEGFR1 and VEGFR2, regulate normal physiological vessel development. The functional role of angiopoietins in tumor angiogenesis, in particular astrocytoma angiogenesis, remains unclear. In this study, we focus on the specific contribution of Ang1 to the vascular growth of glioblastoma multiforme (GBM) and its interactive role with VEGF-A. Subcutaneous and intracranial GBM xenografts were generated using 3 established astrocytoma cell lines (U87, U373, and U343) that were transfected to stably over-express Ang1. GBM xenografts were also generated to express low levels of VEGF-A and high Angl. We found that Ang1 increases the vascular growth of both subcutaneous and intracranial xenografts of GBM by approximately 3-fold. However, the increased vascular growth was only seen in xenografts with concurrent VEGF-A elevation, since decreasing VEGF-A expression resulted in a loss of the pro-angiogenic growth advantage seen with Ang1. Collectively, our data suggest that Ang1 regulates GBM vascularity in a VEGF-A dependent manner, synergizing the initial pro-angiogenic response that is triggered by VEGF-A and promoting the vascular growth of GBM.

Neuropilin-1 in human colon cancer: expression, regulation, and role in induction of angiogenesis

Neuropilin-1 (NRP-1), a recently identified co-receptor for vascular endothelial growth factor, is expressed by several nongastrointestinal tumor types and enhances prostate cancer angiogenesis and growth in preclinical models. We investigated the expression and regulation of NRP-1 and the effect of NRP-1 overexpression on angiogenesis and growth of human colon adenocarcinoma by immunohistochemistry and in situ hybridization. NRP-1 was expressed in 20 of 20 human colon adenocarcinoma specimens but not in the adjacent nonmalignant colonic mucosa. By reverse transcriptase-polymerase chain reaction analysis, NRP-1 mRNA was expressed in seven of seven colon adenocarcinoma cell lines. Subcutaneous xenografts of stably transfected KM12SM/LM2 human colon cancer cells overexpressing NRP-1 led to increased tumor growth and angiogenesis in nude mice. In in vitro assays, conditioned medium from NRP-1-transfected cell lines led to an increase in endothelial cell migration, but did not affect endothelial cell growth. Epidermal growth factor (EGF) led to induction of NRP-1 in human colon adenocarcinoma cells and selective blockade of the epidermal growth factor receptor (EGFR) decreased constitutive and EGF-induced NRP-1 expression. Blockade of the Erk 1/2 and P38 mitogen-activated protein kinase signaling pathways also led to a decrease in constitutive and EGF-induced NRP-1 expression. These findings demonstrate the ubiquitous expression of NRP-1 in human colon cancer and suggest that NRP-1 may contribute to colon cancer angiogenesis and growth. This study also suggests that EGF and mitogen-activated protein kinase signaling pathways play an important role in NRP-1 regulation in colon cancer cells.

Expression of VEGF receptors in cocultured neuroblastoma cells

BACKGROUND

VEGF is best known for its angiogenic properties. We have found that VEGF expression is increased in neuroblastoma cells cocultured with hepatocytes. In addition, we have previously shown that neuroblastoma cells cultured with exogenous VEGF have an increase in the expression of VEGF receptors. Therefore, we hypothesized that the expression of VEGF receptors would be up-regulated in neuroblastoma cells grown in the coculture environment.

MATERIALS AND METHODS

Two neuroblastoma cell lines (IMR-32 or SK-N-DZ) are used. These cells are cultured alone and in a coculture system with hepatocytes. Message for VEGF and the VEGF receptors KDR, flt-1, flt-4, neuropilin 1 (NRP-1), and neuropilin 2 (NRP-2) are measured with RT-PCR. Flt-4, NRP-1, and NRP-2 protein expression is measured with Western blot.

RESULTS

The receptors KDR and flt-1 are not detected in either cell line in either control or coculture conditions. Message for VEGF and flt-4 is significantly increased in the cocultured IMR-32 cells, while that for NRP-1 and NRP-2 is unchanged in these cells. VEGF and its receptors are unchanged in cocultured SK-N-DZ cells.

CONCLUSIONS

Neuroblastoma cells express specific VEGF receptors that are differentially regulated in the different cell lines. These findings suggest that the heterogeneity of neuroblastomas may limit the utility of targeting VEGF and its receptors as sole treatments for the tumor, and that successful therapies will be dependent upon the specific biology of the tumor.

Expression of neuropilin-1 in high-grade dysplasia, invasive cancer, and metastases of the human gastrointestinal tract

Neuropilin-1 (NRP-1) functions as an axonal guidance molecule in the developing nervous system, and recent work has identified NRP-1 up-regulation in several cancers, including neuroblastomas and breast carcinoma. We examined for the first time NRP-1 expression in a large variety of gastrointestinal carcinomas and precursor lesions to determine whether NRP-1 up-regulation correlated with invasive growth in this system. Protein expression and localization of NRP-1 were studied by immunolabeling and semiquantification in >300 dysplastic, invasive, and metastatic lesions of the gastrointestinal tract, and confirmation of NRP-1 protein expression was performed by Western blot analysis on pancreatic cancer cell lines. NRP-1 expression was limited within normal tissues of the gastrointestinal tract, with prominent labeling present only in endothelial cells, pancreatic islet cells, and the most apical colonic epithelium. Invasive cancer of the esophagus, gallbladder, ampulla of Vater, pancreas (endocrine and exocrine), and colon, however, all demonstrated striking NRP-1 expression. NRP-1 was also identified in precursor lesions of gastrointestinal adenocarcinomas, such as Barrett esophagus and colorectal adenomas. Within the spectrum of precursor lesions, a progressive increase in both intensity and area of expression was evident during histologic progression from low-grade to high-grade dysplasia. Notably, the most intense up-regulation of NRP-1 was apparent at or around the point of invasion, with focal expression of NRP-1 at levels equivalent to the invasive cancer (2- to 3-fold increase). Prominent labeling for NRP-1 was apparent in primary invasive cancers, liver metastases, and a subset of lymph node metastases, with a 2- to 3-fold increase of NRP-1 over dysplastic lesions. We conclude that increased expression of NRP-1 occurs in gastrointestinal adenocarcinomas and in a subset of high-grade precursor lesions. This up-regulation appears to parallel invasive behavior and may therefore be used as a potential marker for cancer aggressiveness in this system.

Vascular endothelial growth factor (VEGF) receptor neuropilin-1's distribution in astrocytic tumors

Neuropilin-1 is a VEGF165- and semaphorin receptor expressed by endothelial cells and tumor cells. The specific function of neuropilin-1 is not fully known, but in the developing nervous system neuropilin, as a semaphorin receptor, has been shown to influence neuronal guidance. The expression of neuropilin-1 was studied in low-grade and high-grade astrocytic tumors, the latter characterized by extensive angiogenesis. We examined 20 low-grade astrocytomas (WHO grade II) and 46 glioblastomas (WHO grade IV) immunohistochemically for neuropilin-1, p53 and EGFR. The glioblastomas were according to the p53 and EGFR expression classified as 35 primary--de novo--glioblastomas, 9 secondary glioblastomas, and 2 uncertain cases. Furthermore, the presence of mast cells was evaluated to search for any potential function in angiogenesis. The glioblastomas expressed neuropilin-1 in the endothelial cells of the proliferating vessels and the majority of the glioblastomas had immunoreactive neoplastic astrocytes, with no difference between the glioblastoma subgroups. Six out of twenty of the low-grade astrocytomas were negative in the endothelial cells and 8 out of 20 in the tumor cells for neuropilin-1. Mast cells were observed in the collagen matrix around larger vessels in the leptomeninges, but not adjacent to malignant tumor vessels or as part of the tumor process itself. Increased expression of neuropilin-1 is shown in endothelial cells and in neoplastic astrocytes of glioblastomas. Less neuropilin-1 expression is found in about half of the low-grade astrocytomas in both neoplastic astrocytes and endothelial cells. The results suggest a correlation between neuropilin-1 and vascularity in human astrocytic tumors and a possible role for neuropilin-1 as a receptor for VEGF-induced angiogenesis.

Pancreatic carcinoma cells express neuropilins and vascular endothelial growth factor, but not vascular endothelial growth factor receptors

BACKGROUND

Neuropilins (NRPs) are characterized as coreceptors of vascular endothelial growth factor (VEGF). In the current study, the authors assessed the expression of NRPs, VEGF, and vascular endothelial growth factor receptors (VEGFRs), as well as VEGF-induced cell proliferation, in pancreatic carcinoma cell lines and tissue specimens.

METHODS

Human pancreatic carcinoma cell lines (Panc-1 and MIA PaCa-2), normal human pancreatic ductal epithelial cells (HPDE), and human umbilical vein endothelial cells (HUVECs) were cultured. Human pancreatic adenocarcinoma tissue specimens were also studied. Expression levels of NRPs, VEGFRs, and VEGF were determined by real-time polymerase chain reaction analysis and immunostaining. Cell proliferation was examined using a [3H]thymidine incorporation assay.

RESULTS

Both NRP-1 and NRP-2 were expressed in Panc-1 cells, HPDE cells, and HUVECs but were expressed minimally in MIA PaCa-2 cells. Panc-1 expressed 30 times more NRP-1 mRNA than NRP-2 mRNA. NRP-1 levels in Panc-1 cells were 5.3 times higher than in HPDE cells but were similar to NRP-1 levels in HUVECs. NRP-2 levels in Panc-1 cells were similar to NRP-2 levels in HPDE cells but lower than NRP-2 levels in HUVECs. Expression of all three VEGFRs was observed only in HUVECs. However, VEGF mRNA was detected in all cell types except for HUVECs. NRP-1 immunoreactivity levels were much higher than NRP-2 immunoreactivity levels in Panc-1 and human pancreatic adenocarcinoma tissue specimens, whereas VEGFRs were not detected in either of these two settings. In response to VEGF165, [3H]thymidine incorporation in Panc-1 cells increased significantly (by 61%; P < 0.01). A monoclonal antibody against human NRP-1 significantly blocked VEGF-induced cell proliferation in Panc-1 cells.

CONCLUSIONS

The pancreatic carcinoma cell line Panc-1 and adenocarcinoma tissue specimens expressed high levels of NRP-1 and VEGF, but not VEGFRs, and exogenous VEGF significantly increased NRP-1-mediated, but not VEGFR-mediated, Panc-1 cell proliferation. These data suggested that NRP-1 may be involved in the pathogenesis of pancreatic carcinoma.

Vascular endothelial growth factor expression correlates with matrix metalloproteinases MT1-MMP, MMP-2 and MMP-9 in human glioblastomas

Vascular endothelial growth factor (VEGF) is the major endothelial mitogen in central nervous system neoplasms and it is expressed in 64-95% of glioblastomas (GBMs). Tumour cells are the main source of VEGF in GBMs whereas VEGF receptors (VEGFR-1, its soluble form sVEGFR-1, VEGFR-2 and neuropilin-1) are expressed predominantly by endothelial cells. Infiltrating tumour cells and newly-formed capillaries progress through the extracellular matrix by local proteolysis involving matrix metalloproteinases (MMPs). Recent studies have shown that VEGF expression and bioavailability can be modulated by MMPs. We reported previously that the expression of MT1-MMP in human breast cancer cells was associated with an enhanced VEGF expression. We used quantitative RT-PCR, Western blot, gelatin zymography and immunohistochemistry to study the expression of VEGF, VEGFR-1, VEGFR-2, sVEGFR-1, neuropilin-1, MT1-MMP, MMP-2, MMP-9 and TIMP-2 in 20 human GBMs and 5 normal brains. The expression of these MMPs was markedly increased in most GBMs with excellent correlation between mRNA and protein levels; activated forms of MMP-2 and MMP-9 were present in 8/18 and 7/18 of GBMs. A majority of GBMs (17/20) also expressed high levels of VEGF, as previously reported, with strong correlation between VEGF and MT1-MMP gene expression levels, and double immunostaining showed that VEGF and MT1-MMP peptides co-localize in tumour and endothelial cells. Our results suggest that the interplay between metalloproteinases and VEGF previously described in experimental tumours may also be operative in human GBMs. Because of its dual ability to activate MMP-2 and to up-regulate VEGF, MT1-MMP might be of central importance in the growth of GBMs and represent an interesting target for anti-cancer treatments.

Expression and regulation of the novel vascular endothelial growth factor receptor neuropilin-1 by epidermal growth factor in human pancreatic carcinoma

BACKGROUND

It was recently shown that neuropilin-1 (NRP-1), which was described originally as a receptor for the semaphorins/collapsins (ligands involved in neuronal guidance), is a coreceptor for vascular endothelial growth factor (VEGF) and increases the affinity of specific isoforms of VEGF to its receptor, VEGF-R2.

METHODS

The authors investigated the expression and regulation of NRP-1 in human pancreatic adenocarcinoma specimens and cell lines.

RESULTS

Immunohistochemical analysis revealed that NRP-1 was expressed in 12 of 12 human pancreatic adenocarcinoma specimens but was absent in nonmalignant pancreatic tissue. Northern blot analysis revealed NRP-1 mRNA expression in 8 of 11 human pancreatic adenocarcinoma cell lines. NRP-1 mRNA expression was increased by epidermal growth factor (EGF) but not by tumor necrosis factor alpha in several of the human pancreatic adenocarcinoma cell lines studied. Treating human Panc-48 adenocarcinoma cells with EGF activated Akt and Erk but not P-38. Blockade of the phosphatidylinositol-3 kinase (PI-3K)/Akt, mitogen-activated protein kinase (MAPK)/Erk, or P-38 pathways abrogated EGF-induced NRP-1 expression. Finally, EGF receptor blockade in vivo led to a decrease in NRP-1 expression in an orthotopic model of human pancreatic carcinoma.

CONCLUSIONS

NRP-1 is expressed in most human pancreatic adenocarcinomas and cell lines but not in nonmalignant pancreatic tissue. EGF regulates NRP-1 expression through the PI-3K/Akt and MAPK/Erk signaling pathways, and blockade of the EGF receptor is associated with decreased expression of NRP-1 in vivo. NRP-1 may act as a coreceptor for VEGF in pancreatic carcinoma, as it does in other tumor systems, thereby enhancing angiogenesis and the effect of VEGF on the growth of pancreatic adenocarcinoma.